Let There Be Light

Are high pressure sodium vapour lamps more efficient than LEDs?

The key to answering this question is "Luminous Efficacy", a measure of how well a light source a Watt of electricity into Lumens, a measure of light intensity visible to the human eye.

Today, while clearing some litter at a nearby park, I came across this box -

It was lying on the grass, right below a high-mast lamp. Even though I knew that these sodium vapor lamps consumed a lot of electricity, what struck me was the quantum of light produced by these bulbs. A 400W bulb produces more than 44,000 lumens!

If this makes little sense, just compare it to the standard LED lamps being distributed by the government, in its efforts to being down household electricity  consumption -

In terms of luminous efficacy, one would have thought that the LED lamps are a lot more efficient that any incandescent, power-guzzling bulb. However, in terms of light output (lumens), the sodium vapour lamp produces 110 lumens/W while the LED lights prouduce 114 lumens/W, which is hardly any difference.

If there is not much difference in the efficiency of LED bulbs and sodium-vapour lamps, is there a big difference in cost? The sodium-vapour lamp costs INR 675 per unit while an (unsubsidized) LED lamp costs anywhere between INR 150 and 250. This means that the cost of luminous efficacy is INR 0.16 lm/W/INR for the sodium-vapour lamp and 0.57 lm/W/INR for LEDs.  

This simply means that you are getting 3.5 times more bang for your buck with LEDs, compared to sodium-vapour lamps. So it does make sense to switch to LEDs.

Now, what is the difference is cost between LEDs meantand SVs for high-mast lamps? That would berhaps perhaps be a better comparison of oranges with oranges!

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LINKS

* Energy efficiency of LEDs - http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/led_energy_efficiency.pdf

* https://en.wikipedia.org/wiki/Luminous_efficacy

* 2009 - Toshiba releases 93 lm/W bulbs - http://ledsreview.com/news/367/

Making Bangles, Saving Energy

This was a visit of many firsts – my first visit to the ‘Glass Capital’ of India - Firozabad; my introduction to the process of bangle-making and the first time I have actually seen the results of a energy research project that benefits thousands of people.

Until a few years ago, Firozabad used to be enveloped in a cloud of smoke coming from thousands of coal-fired furnaces. The fact that the city was a mere 40km from the yellowing marbles of the Taj Mahal in Agra, earned it a lot of attention from environmental activists.

In 1994, the Supreme Court imposed restrictions on four major sources of pollution within the Taj Trapezium Zone (TTZ) – automobiles in Agra city, the Mathura Oil Refinery, the Foundries in Agra, and the Glass industry in Firozabad. They were given a deadline and told to either shut down, switch to cleaner fuels or to move out of the 10,400 sq.km TTZ.

Among the hundreds of glass factories in Firozabad agonizing over the SC order, Islam Khan was the first to open the doors of his factory, Express Glass Works (EGW), to researchers seeking to help the industry switch from coal to gas fired furnaces. It was a tough decision – on one hand was the cost of displacing people associated with EGW for over three generations, and other the other, was the economic imperatives -- a coal furnace costs less than Rs. 200,000; for a 30% reduction in energy consumption, he had to install a facility that cost Rs. 3000,000! Clearly, this defied business logic, so Khan had to be persuaded with generous subsidies from SDC and promises of international technical support through TERI.

When the gas furnace was finally ready, one huge problem still remained – EGW was famous for its blood-red “Lal Anju” bangles. Somehow the clean-fuel technology had robbed the factory of its USP. TERI tried to solve the problem by bringing in Indian and international experts but nothing worked. Ultimately, Islam Khan had to use his own ingenuity and skills to bring about a consistent, deep red into his bangles.

Today the factory is veritable beehive of activity. More than a hundred workers go about their work – feeding the ovens with sand, caustic soda and other chemicals; scooping out ladles of glowing, molten glass; adding strips of color and softening them again for the ustads who transfer fine threads of glass on to a rotating shaft, resulting in long glass springs which are then split using diamond tipped cutters.

Ultimately what exits the factory gates are the “spilt” bangles. These are then sent to smaller shops where they are fused, glazed and polished in smaller ovens (paka-bhattis) before going out to the retail outlets.

Thanks to the Supreme Court directive, more than 40 units in Firozabad have now switched to the cleaner, gas-fired furnaces. The workers continue to work in difficult conditions but at least they are able to retain their jobs in a city where the air is lot cleaner than it used to be.

The main furnace

Steady hands that turn molten glass into bangle spirals

Splitting the spirals
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References & Links:

• Glass apart - Chitra Subramanyam, India Today June 26, 2008
• The Taj Mahal: Pollution and Tourism - TED Case Studies, 2002